Field of the Disclosure
The present disclosure relates to a display device, and more particularly, to a driver integrated circuit for external compensation, a display device including the driver integrated circuit, and a data correction method of the display device.
Description of the Background
Various types of panel displays have been developed and sold. Among the various types of panel displays, an electroluminescent display is classified into an inorganic electroluminescent display and an organic electroluminescent display depending on a material of an emission layer. In particular, an active matrix organic light emitting diode (OLED) display includes a plurality of OLEDs capable of emitting light by themselves and has many advantages, such as fast response time, high emission efficiency, high luminance, wide viewing angle, and the like.
An OLED serving as a self-emitting element includes an anode electrode, a cathode electrode, and an organic compound layer between the anode electrode and the cathode electrode. The organic compound layer includes a hole injection layer HIL, a hole transport layer HTL, an emission layer EML, an electron transport layer ETL, and an electron injection layer EIL. When power (voltage) is applied to the anode electrode and the cathode electrode, holes passing through the hole transport layer HTL and electrons passing through the electron transport layer ETL move to the emission layer EML and form excitons. As a result, the emission layer EML generates visible light.
An OLED display includes a plurality of pixels, each including an OLED and a thin film transistor (TFT) that adjusts a luminance of an image implemented on the pixels based on a grayscale of image data. The driving TFT controls a driving current flowing into the OLED depending on a voltage (hereinafter, referred to as “a gate-to-source voltage”) between a gate electrode and a source electrode of the driving TFT. The amount of light emitted by the OLED is determined depending on the driving current of the OLED, and the luminance of the image is determined depending on the amount of light emitted by the OLED.
In general, when a driving TFT operates in a saturation region, a driving current Ids flowing between a drain electrode and a source electrode of the driving TFT is expressed by the following Equation 1.Ids=½*(μ*C*W/L)*(Vgs−Vth)2  [Equation 1]
In the above Equation 1, μ is electron mobility, C is a capacitance of a gate insulating layer, W is a channel width of the driving TFT, and L is a channel length of the driving TFT. In addition, Vgs is a voltage between a gate electrode and a source electrode of the driving TFT, and Vth is a threshold voltage (or a critical voltage) of the driving TFT. A gate-to-source voltage Vgs of the driving TFT may be a voltage differential between a data voltage and a reference voltage in accordance with a pixel structure. The data voltage is an analog voltage corresponding to a grayscale of image data, and the reference voltage is a fixed voltage. Therefore, the gate-to-source voltage Vgs of the driving TFT is programmed or set depending on the data voltage. Then, the driving current Ids is determined depending on the programmed gate-to-source voltage Vgs.
Electrical characteristics of the pixel, such as the threshold voltage Vth and the electron mobility μ of the driving TFT and a threshold voltage of the OLED, may be factors determining the amount of driving current Ids of the driving TFT. Therefore, all the pixels should have the same electrical characteristics. However, a variation in the electrical characteristics between the pixels may be caused by various factors such as manufacturing process characteristics and time-varying characteristics. The variation in the electrical characteristics between the pixels may lead to a luminance variation, and it is difficult to implement desired images or meet image quality requirements.
In order to compensate for the luminance variation between the pixels, there are so-called external compensation techniques for sensing electrical characteristics of the pixels and correcting (or compensating for) an input image based on the sensing result. In order to compensate for the luminance variation, a current change by an amount of Δy has to be ensured when the data voltage applied to the pixel is changed by an amount of “Δx”. Thus, the external compensation technique is to implement the same (or effectively the same) brightness by calculating “Δx” for each pixel and applying the same driving current to the OLED. Namely, the external compensation technique may be implemented to adjust the gray levels so that the pixels have the same or effectively the same brightness.
In order to implement the external compensation technique, a sensor for sensing electrical characteristics of the pixels and an analog-to-digital converter (ADC) for converting analog sensing data input from the sensor into digital sensing data are required.
The digital sensing data output from the ADC may be distorted by various causes. Among the various causes, the distortion due to a characteristic variation between the ADCs is particularly problematic. When the digital sensing data is distorted, a luminance variation resulting from a difference in the electrical characteristics between the pixels cannot be compensated properly.